Corrupt bishop, when caught in action (7)
I believe the answer is:
debased
'corrupt' is the definition.
('debased' can be similar in meaning to 'corrupt')
'bishop when caught in action' is the wordplay.
'bishop' becomes 'b' (abbreviation used in chess).
'when' becomes 'as'.
'caught in' indicates putting letters inside.
'action' becomes 'deed' (deed is a kind of action).
'b'+'as'='bas'
'bas' going within 'deed' is 'DEBASED'.
(Other definitions for debased that I've seen before include "shamed" , "corrupted" , "Corrupt" , "Lowered, depreciated" , "Lowered in value" .)